This invention relates generally to an apparatus and method for measuring the viscosity of liquids, and more particularly, an apparatus and methods for measuring the viscosity of both Newtonian fluids and non-Newtonian fluids over a wide range of shears.
Viscometers currently available may be grouped into three broad categories: 1) capillary tube viscometers; 2) rotating viscometers; and 3) falling ball or needle viscometers. Most of these techniques yield viscosity measurements at a specified, constant shear rate; for measuring Newtonian fluids, i.e., fluids where the viscosity does not vary with shear rate, these techniques are satisfactory. However, for determining the viscosity of non-Newtonian fluids, i.e., where the viscosity varies with shear rate, in order to measure the viscosity over a range of shear rates, one needs to make repetitive measurements while varying either the pressure in the reservoir tank of capillary tube viscometers, the rotating speed of the cup/cone in rotating viscometers, or the density of the falling objects. Such operations can make these viscosity-measurement techniques difficult, time consuming and labor intensive.
With particular regard to measuring the viscosity of a non-Newtonian fluid, such as blood, there are a number of patents relating to blood viscosity measuring apparatus and methods. See for example, U.S. Pat. Nos.: 3,342,063 (Smythe et al.); 3,720,097 (Kron); 3,999,538 (Philpot, Jr.); 4,083,363 (Philpot); 4,149,405 (Ringrose); 4,165,632 (Weber, et. al.); 4,517,830 (Gunn, deceased, et. al.); 4,519,239 (Kiesewetter, et. al.); 4,554,821 (Kiesewetter, et. al.); 4,858,127 (Kron, et. al.); 4,884,577 (Merrill); 4,947,678 (Hori et al.); 5,181,415 (Esvan et al.); 5,257,529 (Taniguchi et al.); 5,271,398 (Schlain et al.); and 5,447,440 (Davis, et. al.).
The Smythe ""063 patent discloses an apparatus for measuring the viscosity of a blood sample based on the pressure detected in a conduit containing the blood sample. The Kron ""097 patent discloses a method and apparatus for determining the blood viscosity using a flowmeter, a pressure source and a pressure transducer. The Philpot ""538 patent discloses a method of determining blood viscosity by withdrawing blood from the vein at a constant pressure for a predetermined time period and from the volume of blood withdrawn. The Philpot ""363 patent discloses an apparatus for determining blood viscosity using a hollow needle, a means for withdrawing and collecting blood from the vein via the hollow needle, a negative pressure measuring device and a timing device. The Ringrose ""405 patent discloses a method for measuring the viscosity of blood by placing a sample of it on a support and directing a beam of light through the sample and then detecting the reflected light while vibrating the support at a given frequency and amplitude. The Weber ""632 patent discloses a method and apparatus for determining the fluidity of blood by drawing the blood through a capillary tube measuring cell into a reservoir and then returning the blood back through the tube at a constant flow velocity and with the pressure difference between the ends of the capillary tube being directly related to the blood viscosity. The Gunn ""830 patent discloses an apparatus for determining blood viscosity that utilizes a transparent hollow tube, a needle at one end, a plunger at the other end for creating a vacuum to extract a predetermined amount and an apertured weight member that is movable within the tube and is movable by gravity at a rate that is a function of the viscosity of the blood. The Kiesewetter ""239 patent discloses an apparatus for determining the flow shear stress of suspensions, principally blood, using a measuring chamber comprised of a passage configuration that simulates the natural microcirculation of capillary passages in a being. The Kiesewetter ""821 patent discloses another apparatus for determining the viscosity of fluids, particularly blood, that includes the use of two parallel branches of a flow loop in combination with a flow rate measuring device for measuring the flow in one of the branches for determining the blood viscosity. The Kron ""127 patent discloses an apparatus and method for determining blood viscosity of a blood sample over a wide range of shear rates. The Merrill ""577 patent discloses an apparatus and method for determining the blood viscosity of a blood sample using a hollow column in fluid communication with a chamber containing a porous bed and means for measuring the blood flow rate within the column. The Hori ""678 patent discloses a method for measurement of the viscosity change in blood by disposing a temperature sensor in the blood flow and stimulating the blood so as to cause a viscosity change. The Esvan ""415 patent discloses an apparatus that detects the change in viscosity of a blood sample based on the relative slip of a drive element and a driven element, which holds the blood sample, that are rotated. The Taniguchi ""529 patent discloses a method and apparatus for determining the viscosity of liquids, e.g., a blood sample, utilizing a pair of vertically-aligned tubes coupled together via fine tubes while using a pressure sensor to measure the change of an internal tube pressure with the passage of time and the change of flow rate of the blood. The Bedingham ""328 patent discloses an intravascular blood parameter sensing system that uses a catheter and probe having a plurality of sensors (e.g., an O2 sensor, CO2 sensor, etc.) for measuring particular blood parameters in vivo. The Schlain ""398 patent discloses a intra-vessel method and apparatus for detecting undesirable wall effect on blood parameter sensors and for moving such sensors to reduce or eliminate the wall effect. The Davis ""440 patent discloses an apparatus for conducting a variety of assays that are responsive to a change in the viscosity of a sample fluid, e.g., blood.
Viscosity measuring devices and methods for fluids in general are well-known. See for example, U.S. Pat. Nos.: 1,810,992 (Dallwitz-Wegner); 2,343,061 (Irany); 2,696,734 (Brunstrum et al.); 2,700,891 (Shafer); 2,934,944 (Eolkin); 3,071,961 (Heigl et al.); 3,116,630 (Piros); 3,137,161 (Lewis et al.); 3,138,950 (Welty et al.); 3,277,694 (Cannon et al.); 3,286,511 (Harkness); 3,435,665 (Tzentis); 3,520,179 (Reed); 3,604,247 (Gramain et al.); 3,666,999 (Moreland, Jr. et al.); 3,680,362 (Geerdes et al.); 3,699,804 (Gassmann et al.); 3,713,328 (Aritomi); 3,782,173 (Van Vessem et al.) 3,864,962 (Stark et al.); 3,908,441 (Virloget); 3,952,577 (Hayes et al.); 3,990,295 (Renovanz et al.); 4,149,405 (Ringrose); 4,302,965 (Johnson et al.); 4,426,878 (Price et al.); 4,432,761 (Dawe); 4,616,503 (Plungis et al.); 4,637,250 (Irvine, Jr. et al.); 4,680,957 (Dodd); 4,680,958 (Ruelle et al.); 4,750,351 (Ball); 4,856,322 (Langrick et al.); 4,899,575 (Chu et al.); 5,142,899 (Park et al.); 5,222,497 (Ono); 5,224,375 (You et al.); 5,257,529 (Taniguchi et al.); 5,327,778 (Park); and 5,365,776 (Lehmann et al.).
A device called the xe2x80x9cHevimet 40xe2x80x9d has recently been advertised at www.hevimet.freeserve.co.uk. The Hevimet 40 device is stated to be a whole blood and plasma viscometer that tracks the meniscus of a blood sample that falls due to gravity through a capillary. While the Hevimet 40 device may be generally suitable for some whole blood or blood plasma viscosity determinations, it appears to exhibit several significant drawbacks. For example, among other things, the Hevimet 40 device appears to require the use of anti-coagulants. Moreover, this device relies on the assumption that the circulatory characteristics of the blood sample are for a period of 3 hours the same as that for the patient""s circulating blood. That assumption may not be completely valid.
The following U.S. patents disclose viscosity or flow measuring devices, or liquid level detecting devices using optical monitoring: U.S. Pat. Nos. 3,908,441 (Virloget); 5,099,698 (Kath, et. al.); 5,333,497 (Br nd Dag A. et al.). The Virloget ""441 patent discloses a device for use in viscometer that detects the level of a liquid in a transparent tube using photodetection. The Kath ""698 patent discloses an apparatus for optically scanning a rotameter flow gauge and determining the position of a float therein. The Br nd Dag A. ""497 patent discloses a method and apparatus for continuous measurement of liquid flow velocity of two risers by a charge coupled device (CCD) sensor.
A statutory invention registration, H93 (Matta et al.) discloses an apparatus and method for measuring elongational viscosity of a test fluid using a movie or video camera to monitor a drop of the fluid under test.
Notwithstanding the existence of the foregoing technology, a need remains for an apparatus and method for obtaining the viscosity of both Newtonian fluids and non-Newtonian fluids (e.g., blood) over a range of shears, including low shear ranges (e.g., 0.1sxe2x88x921), and where flow rate and pressure drop measurements can be avoided and where the viscosity determination can be conducted in a short span of time.
Accordingly, it is an object of the present invention to substantially obviate one or more of the problems associated with the related art.
It is an object of the present invention to provide an apparatus and method for obtaining the viscosity of both Newtonian fluids and non-Newtonian fluids over a range of shear rates in real time.
It is another object of the present invention to provide an apparatus and method for obtaining the viscosity of non-Newtonian fluids (e.g., circulating blood of a living being) over a range of shears, including low shear rates (e.g., 0.1sxe2x88x921).
It is still another object of the present invention to provide an apparatus and method for obtaining the viscosity of both Newtonian fluids and non-Newtonian fluids where flow rate and pressure drop measurements can be avoided.
It is still another object of the present invention to provide an apparatus and method that detects the column heights of a plurality of fluid columns in a corresponding plurality of transparent containers substantially simultaneously while using a single detector.
These and other objects of the invention can be achieved by an apparatus for effecting the viscosity measurement of Newtonian and non-Newtonian fluids over a range of shear rates. The apparatus comprises: a pair of tubes having respective ends coupled to a source of Newtonian or non-Newtonian fluid and wherein each of the tubes comprises a respective capillary tube and wherein the capillary tubes have different lengths; a respective valve in each of the tubes for controlling the fluid flow from the fluid source; an analyzer, coupled to the valves, for controlling the valves to permit the flow of fluid into the pair of tubes whereupon the fluid in each of the pair of tubes assumes the same initial position with respect to a reference position. The analyzer is arranged for operating the valves so that the position of the fluid in each of the tubes changes away from the same initial position. The analyzer is also arranged for monitoring the fluid position change in each of the tubes and calculating the viscosity of the fluid based thereon.
These and other objects of the invention can also be achieved by an apparatus for monitoring the level of a plurality of columns of fluid in a respective plurality of transparent containers substantially simultaneously. The apparatus comprises: an optical source of light for each one of the plurality of columns of fluid and wherein each of the optical sources emits a respective light ray at its corresponding transparent container; and a single detector for detecting at least a portion of each respective light ray that impinges on the corresponding transparent container substantially simultaneously.
These and other objects of the invention can also be achieved by a method for effecting the viscosity measurement of Newtonian and non-Newtonian fluids over a range of shear rates, said method comprising the steps of: (a) providing a pair of tubes each having an end coupled to a source of Newtonian or non-Newtonian fluid and each tube comprising respective capillary tube portions and wherein each of the respective capillary tube portions have lengths different from each other and wherein each of the tubes comprise a valve; (b) activating the respective valves to generate a respective fluid flow from the source through each of the pair of tubes; (c) de-activating the respective valves to establish a same initial position of fluid in each of the tubes with respect to a reference position; (d) re-activating the respective valves so that the position of fluid in each of the tubes changes away from the same initial position; (e) monitoring the fluid position change in each of said tubes; and (f) calculating the viscosity of the fluid based thereon.
These and other objects of the invention can also be achieved by a method for monitoring the level of a plurality of columns of fluid in a respective plurality of transparent containers. The method comprises the steps of: (a) directing a respective ray of light at its corresponding transparent container; and (b) detecting at least a portion of each of the respective light rays that impinges upon the transparent container and wherein the at least a portion of each of the respective light rays that are detected comprises that portion of the light rays that does not encounter any fluid in the transparent containers.